Conventionally, the heat treatment of the above-described structural member is normally carried out by quench-and-temper. After welding is performed, re-solution treatment and aging treatment are carried out.
However, when the above-described re-solution treatment is done, the welded structural member is deformed by residual stress or gravitation. To prevent the deformation, considerably large-scale, firm constraint is required. Even a structural member which does not involve welding has far lower toughness as compared with a member heat-treated in accordance with the present invention.
The present invention was made in view of the above situation. Accordingly, an object of the present invention is to provide a method of producing a structural member in which the deformation occurring during heat treatment is prevented and the toughness is significantly improved.